A capsule endoscope (CE) is one of the most common non-invasive clinical tools in the evaluation of gastrointestinal (GI) tract disease. Currently millions of CEs have been used worldwide to diagnose the small-bowel and to assess GI tract performance. Specifically, CE intervention has been adopted when gastroesophageal reflux disease, obscure gastrointestinal bleeding, Crohn's disease, and polyposis syndromes are indicated. Numerous clinical records and multiple studies have proven that CE intervention is superior to radiologic interventions and push endoscopy because it is non-invasive, has relatively small dimensions, features high image quality, and provides direct visualization of the tissue. Researchers have been looking to expand this method into new domains due to increases in chronic diseases and an aging population.
In the past, the movement of the CE through the GI tract was accepted as being passive and a function of intestine peristalsis. However, in order to complete more accurate diagnostics and treatment of chronic diseases, it is desirable for CEs to offer controllable locomotion, long-term (multi-week) data collection, and drug delivery function. A variety of locomotion systems for CEs have been developed by different methods such as shape memory alloy legs, magnetic drive, and earthworm-like locomotive mechanisms. The CE's capability to acquire long-term physiological indexes is still limited, however, because of its inability to remain in-vivo long-term attachment. The gastrointestinal wall is irregular, slippery, chemically corrosive, and physiologically active due to peristalsis. No traditional technologies enable effective adhesion to such a surface for a prolonged period of time without causing damage or bleeding, and premature loss of the capsule during sensing periods has often been reported. Mucosal adhesive patches may be a potential solution for the long-term attachment requirement, as studied by several research groups. Research groups have shown that high static friction could be created between a colonoscopic device and the GI wall due to mucoadhesion. Mucoadhesive patches have been tested and assembled with a release mechanism in the CEs. Additionally, it has been shown that with 5N preload force, 110 min stable anchoring could be achieved for a 10 mm diameter mucoadhesive patch. These improvements are incremental, however, and still do not enable multi-day or weeks long attachment.
Better clinical outcomes could be obtained if physicians could obtain continuous readings of the small intestine from stationary CEs. Also, in addition to data collection and image recording, long-term attachment may provide other possible functions to CE such as tissue manipulation and drug delivery.
Since the introduction of wireless capsule endoscopy (WCE) in 2000, research communities around the world have been developing miniature swallowable devices that have potential to replace invasive diagnostic tools. Since the WCE's first approval by the Food and Drug Administration (FDA) in 2001, capsule technology has evolved to be used by millions and said to be the most effective diagnostic technique in the small bowel, as well as a subject of worldwide research focused on developing noninvasive diagnostic and therapeutic devices. WCEs such as the PillCam® SB3 (Given Imaging Ltd—now Medtronic Inc., Minnesota, USA)), MiroCam™ v2 (IntroMedic Co, Seoul, South Korea) are clinically available and have established WCE as the gold standard in diagnosing illnesses in the small intestine. Technologies such as miniature integrated circuits (IC) and sensors have become readily available, which has opened the door for development of miniature ingestible devices that can replace standard wearable sensors.
Miniaturizing such technologies and maximizing their efficacy in a zero gravity environment will be a critical step in pursuing distant space exploration. For example, with the coming advent of long-distance human space flights, regular monitoring of astronaut health parameters will be critical to achieve successful and safe missions. The twenty-first century has already seen a paradigm shift in medical technology: groups in both academia and industry are focusing research on developing minimally invasive medical devices for diagnostics, biopsy, therapeutics, and surgery. In the 1980's, the National Aeronautics and Space Administration, NASA, took interest in ingestible sensing technologies, a telemetry capsule used for monitoring body core temperature that is now known as the CorTemp® Ingestible Core Body Temperature Sensor (HQ Inc., Florida, USA). The product of a partnership between the Johns Hopkins University, the Goddard Space Flight Center, and licensing of HQ Inc., the sensor was developed to obtain real time body temperature readings of athletes and astronauts for the prevention of heat related illness (www.spinoffinasa.gov). Used in a number of applications ranging from monitoring athlete core temperature during training, to sleep studies, to monitoring John Glenn's temperature during his final days in space, the device is a prime example of the applicability of a swallowable “smart” device. Gant et al. conducted a study in 2006 involving 10 human subjects who performed physical exercise while having ingested the CorTemp® capsule and reported the temperature measurements to be accurate and reliable. Telemetry capsules like the CorTemp® have been said to be valid tools for assessment of core body temperature. The success of CorTemp®, a sensor able to gather data for less than 24 hours while passing through digestive system, suggests that a similar, but much longer duration system could be very useful.
In recent years, the primary need for astronaut health monitoring is associated with service on board the International Space Station (ISS). Astronauts in the ISS have access to sensors such as Blood Pressure/Electrocardiographs (BP/ECG), Heart Rate Monitor 2 (HRM2), acoustic dosimeters, Crew Passive Dosimeters (CPD), and a Tissue Equivalent Proportional Counter (TEPC). The HRM2 is a wearable technology consisting of a watch, transmitter, and chest strap. These devices are assigned to each crew member. The devices record heart rate data which eventually becomes available for downlink and can be reviewed by flight surgeons for diagnosis. The CPD is used to measure radiation exposure and is required to be worn by each member of the United States crew, with other countries having their own version of the sensor. Utilizing sensory devices which are worn as straps or carried is not an ideal method of monitoring astronaut safety during long term missions. Such devices may inhibit motion, are uncomfortable to wear, require maintenance, and interfere with daily activities.